The present invention relates to a circuit breaker, such as a molded case circuit breaker for actuating and stopping an electric motor and protecting it from overcurrent, and more specifically, to an assembly structure of a contact opening and closing mechanism therefor.
An assembly structure such as that shown in FIG. 4 is known as the circuit breaker referred to above. In FIG. 4, reference numeral 1 denotes a circuit breaker case as a resin molded article comprising a lower case 1a and an upper cover 1b, 2 is a power-side main circuit terminal corresponding to each pole, and 3 is a load-side main circuit terminal. The lower case 1a has a main circuit contact section integrated thereinto and comprising an assembly of fixed contact shoes 4 and 5 connected to the corresponding main circuit terminals, a movable contact shoe 6 bridging the fixed contact shoes 4 and 5, a contact spring 7, a contact shoe holder 8, and arc extinguishing plates 9.
In addition, the upper cover 1b includes an opening and closing lever 10 made of an insulating material and having a journaled rear end and a tip facing a top surface of the contact shoe holder 8, an opening and closing handle 11 projecting from a top surface of the upper cover 1b, a contact opening and closing mechanism section 12 linking between the opening and closing handle 11 and the opening and closing lever 10, an overcurrent tripping device 13 including a thermal tripping device 13a operating in response to a load current through the main circuit and an electromagnetic tripping device 13b operating instantaneously in response to a short circuit current, and others. All these components are integrated into the upper cover 1b. 
In this case, the contact opening and closing mechanism section 12 of the conventional circuit breaker comprises an assembly of a toggle link that couples two links together in the form of xe2x80x9cVxe2x80x9d in such a manner as to sandwich a toggle shaft in a vertical direction of the circuit breaker, to link between the opening and closing handle 11 and the opening and closing lever 10, an opening and closing spring or a main spring extending between the toggle link and a lever of the opening and closing handle 11, and a latch with which the overcurrent tripping device 13 is linked via a trip cross bar (not shown).
The opening and closing operations of such a circuit breaker are well known. When the opening and closing handle 11 is manually operated to the ON side, accumulated force from the opening and closing spring lifts the opening and closing lever 10. This causes the movable contact shoe 6, urged by the contact spring 7, to rise with the holder 8 to bridge the fixed contact shoes 4 and 5. In this contact-closed state, a main circuit current flows from the main circuit terminal 2 through the fixed contact shoe 4, the movable contact shoe 6, the fixed contact shoe 5, and the overcurrent tripping device 13 to the main circuit terminal 3.
Additionally, when the opening and closing handle 11 is operated to the OFF position, the accumulated force of the opening and closing spring of the contact opening and closing mechanism section 12 moves the toggle link reversely to drive the opening and closing lever 10 clockwise from a receding position to push the movable contact shoe 6 downward against the force of the contact spring 7 together with the holder 8, thereby separating the movable contact shoe 6 from the fixed contact shoes 4 and 5 to open the main circuit contact. On the other hand, when an overcurrent or a short-circuit current flows through the main circuit in a conductive state, the overcurrent tripping device 13 operates to release the latch of the contact opening and closing mechanism section 12 to drive the opening and closing lever 10 counterclockwise by the accumulated force of the opening and closing spring. Thus, the movable contact shoe 6 is opened to shut off the main circuit current, i.e. tripping operation.
The above-described conventional circuit breaker structure has problems in regard to the external dimensions of the entire circuit breaker, manual opening and closing operations, and a circuit opening operation.
(1) In the structure shown in FIG. 4, which incorporates the bridging contact-shoe type main circuit contact section located at the bottom of the case 1, and the opening and closing lever 10, the opening and closing handle 11, the contact opening and closing mechanism section 12 and other components located above the main circuit contact section, the entire circuit breaker has a large height H. In particular, if the toggle link of the contact opening and closing mechanism section 12 comprises two links coupled together in the form of a xe2x80x9cVxe2x80x9d in the vertical direction of the circuit breaker, the toggle link has a large height in an extended state, and moves over a wide range when each link, which has been extended, is bent and moved reversely. Consequently, it is difficult to design a small and compact circuit breaker.
(2) Additionally, in the conventional circuit breaker, when the main circuit contact shoe is closed as shown in FIG. 4, a tip of the opening and closing lever 10 abuts against a top surface of the contact shoe holder 8. When the contact shoes are then opened, an opening and closing spring force from the contact opening and closing mechanism section 12 is applied to the opening and closing lever 10 as a static pressure to push the top surface of the contact shoe holder 8 downward, which has been pressed upward by the contact spring 7, thereby opening the movable contact shoe 6. Thus, if the contacts of the fixed and movable contact shoes have been welded or fixed together due to conduction of a high current, an error in the shutting-off operation may occur. For example, the movable contact shoe may not open or its opening may be delayed. To prevent such error, it is contemplated that the opening and closing spring integrated into the contact opening and closing mechanism section 12 may be enhanced. A stronger force of the opening and closing spring, however, results in the necessity of a stronger force for manually operating the opening and closing handle 11, thereby preventing a user from operating the circuit breaker easily.
The present invention has been made in view of the above points, and it is an object of the invention to solve the above-described problems and to provide a circuit breaker with an improved contact opening and closing mechanism that serves to reduce the size of the circuit breaker, to simplify circuit-opening operations and to facilitate operations.
Other objects and advantages of the invention will be apparent from the following description of the invention.
In order to attain the above object, the present invention provides a circuit breaker comprising a main circuit contact section disposed in a case at a bottom thereof and including an assembly of a fixed contact shoe, a movable contact shoe held in a contact shoe holder, and a contact spring that presses and urges the movable contact shoe toward the fixed contact shoe; a movable opening and closing lever located above the main circuit contact section and having a journaled rear end and a tip located at a portion facing a top surface of the holder; a contact opening and closing mechanism also located above the main circuit contact section and including a combination of a toggle link linked with the opening and closing lever, an opening and closing handle, an opening and closing spring extending between a handle lever for the opening and closing handle and the toggle link, and a latch linked with the toggle link; and an overcurrent tripping device located above the main circuit contact section to detect an overcurrent through a main circuit to release the latch.
In the first aspect of the invention, the toggle link comprises a first link having a lower end coupled to the opening and closing lever to extend to a toggle shaft located above, and a second link extending between the toggle shaft and the latch in such a manner as to overlap the first link in a V-form, with the opening and closing spring extending between the toggle shaft and a tip of the handle lever coupled to the opening and closing handle to extend downward.
As compared with the conventional structure wherein the two vertically-arranged links are coupled together in the V-form and extended or bent to operate the opening and closing lever in an opening or closing direction by pivoting, the above configuration serves to reduce the space occupied by the contact opening and closing mechanism section in the height direction of the circuit breaker, making the entire circuit breaker more compact.
Additionally, according to the second aspect of the present invention, the circuit breaker according to the first aspect is set so that when the movable contact shoe is closed, a gap is formed between the top surface of the movable holder of the main circuit contact section and the tip of the opposite opening and closing lever. Accordingly, when the circuit breaker is opened, the tip of the opening and closing lever, pivoted due the force of the opening and closing spring, comes to abut against the top surface of the contact shoe holder of the main circuit contact section to apply a dynamic impact force thereto to open the movable contact shoe.
Thus, if the same spring force of the opening and closing spring is assumed to be applied to the opening and closing lever, a force that pushes the contact shoe holder to open the movable contact shoe is much stronger when it takes the form of a dynamic impact force rather than a static pressure. Consequently, even if the contacts of the fixed and movable contact shoes are fixed or welded together, the movable contact shoe can be reliably separated from the fixed contact shoe to ensure more reliable operation.
Further, according to the third aspect of the present invention, the circuit breaker according to the first aspect has a supplementary spring that helps the opening and closing spring and presses the opening and closing lever toward the contact shoe holder when the main circuit contact is opened.
With such a configuration, the supplementary spring acts on the top surface of the opening and closing lever as a push-in force to offset the force of the contact spring pressing and urging the movable contact shoe from below. Accordingly, the movable contact shoe can be driven from a closed position to an open position, effectively by using the accumulated force of the opening and closing spring as a main spring without requiring of a strong force to operate the opening and closing handle, thereby facilitating the operations required to open the circuit breaker. Additionally, when the circuit breaker is closed, if the opening and closing lever stands by in such a manner that its tip is spaced from the contact shoe holder as explained before, the force from the supplementary spring is prevented from interfering with the contact spring of the movable contact shoe, thereby providing the sufficient contact pressure between the fixed contact shoe and the movable contact shoe.
In the fourth aspect of the invention, the supplementary spring in the third aspect has one end coupled to a supplementary push-in lever that slides over a cam surface formed at a top surface of the opening and closing lever to drive the supplementary lever to apply a push-in force to the opening and closing lever when the main circuit contact is opened.
With such a configuration, when the circuit breaker is opened, the force of the supplementary spring acts on the top surface of the opening and closing lever via the supplementary lever as a push-in force to offset the force of the contact spring for pressing and driving the movable contact shoe from below. Accordingly, the movable contact shoe can be driven from the closed position to the open position by effectively using the accumulated force of the opening and closing spring as a main spring without requiring a strong force to operate the opening and closing handle, thereby facilitating operations required to open the circuit breaker.